Caption: Smooth muscle fibres. Coloured scanning electron micrograph (SEM) of a freeze-fractured bundle of smooth muscle fibres (pink). A blood vessel (red) is at top left. The fracture plane cutting across the smooth muscle fibres has revealed the smaller fibres within the larger fibres. Smooth muscle is found in places like the digestive system and in blood vessels. It is not under voluntary control, instead being controlled by the autonommic nervous system and hormones. It produces slow, long-term contractions.